In modern direct fuel injection engines, such as diesels, it is known to use one or more solenoid actuated devices to control the volume and timing of the fuel supplied to the fuel injectors associated with each combustion chamber. Such solenoid fuel metering devices are preferably electronically controlled and allow the extremely precise metering of fuel necessary to achieve optimum engine performance and low emissions. Fuel metering solenoids must be extremely rugged in order to function properly in the engine environment over a long service life, and they must be able to operate at relatively high fuel pressures.
In order to ensure the factory-set performance characteristics of the engine are not altered by a mechanic or operator after the engine is sold, it is desirable to construct the fuel metering devices to prevent or discourage any tampering therewith.
A prior art fuel metering solenoid stator, as seen in FIG. 1, comprises two large metal components: a casing 100 which houses a solenoid bobbin assembly, and a tubular metal plunger guide 102 with an integral top plate 104. The stator is assembled by inserting the bobbin assembly into a cavity formed in the lower surface of the casing 100, placing mold cores in alignment with three apertures 106,108 in the top of the casing, and pouring or injecting a liquid plastic into the cavity to surround the bobbin assembly and mold cores. The mold cores are removed to leave three holes 110,112 passing completely through the casing 100, and the plunger guide 102 is inserted downwardly through the large, center hole 110 so that it passes through the center of the bobbin assembly. Bolts are inserted upwardly through the two smaller holes 112 passing adjacent the outside of the bobbin and engage threaded holes 114 in the top plate 104 to secure the top plate to the casing and the entire assembly to an engine (not shown). An electrical connector 116 for supplying current to the bobbin wire exits the side of the casing.
A metering plunger (not shown) is inserted upwardly into the bore 118 of the plunger guide 102 from below and a spring (not shown) is disposed in the upper end of the guide 102 to bias the plunger downwardly. When the solenoid stator is energized, the magnetic field generated thereby draws the plunger upward to alternatively open and close a metering orifice below the stator assembly.
This prior art stator assembly requires a significant amount of precision machining and assembly, and therefore is relatively expensive to produce.